Method and apparatus for testing high pressure compressor components and the like



8, 1963 w. R. CROOKS 3,091,116

METHOD AND APPARATUS FOR TESTING HIGH PRESSURE COMPRESSOR COMPONENTS ANDTHE LIKE Filed March 26 1962 May 2 INVENTOR. WILLIAM R. CRooKs @mfkATTORNEYS tires This invention relates to a method and apparatusproductive of very high pressures for testing the performance andstrength of cylinders and other components of gas compressors at veryhigh pressures.

At the present time the chemical industry utilizes multistagereciprocating compressors to compress ethylene gas to about 30,000 to35,000 p.s.i.g. in the manufacture of polyethylene plastics. Theory andsome development testing indicate that quality might be improved and thecosts of the process reduced if the compression pressures at whichpolymerization takes place could be raised to nearer 100,000 p.s.i.g.The development of the higher pressure process has been slowed due tothe mechanical limitations of compressors at these high pressures.

The lack of test facilities and production equipment operative at thesevery high pressures does not allow compressor manufacturers to conductresearch on compressor components suitable for the very high pressuresand has delayed the availability of compressors to the plastics industryas Well as to others for whom a machine of this nature might be useful.

Up to the present time, testing of valves and cylinders in high pressurecompressors has been largely a matter of building the components,assembling them into working units without prior testing, and notingtheir behavior when the compressor is on stream.

Due to gas compressibility from a large volume at atmospheric pressureto a relatively minute volume at very high pressures, the compressor atone stroke or operation cannot sufliciently reduce the volume to obtainthe desired pressure.

A compressor is further limited by the dilference between its supply andexhaust pressures in conjunction with gas compressibility. Thus, incommercial practice several compressors are staged with the firstcompressor discharging to the supply of the second, with the seconddischarging to the supply of the third, with the third discharging tothe supply of the fourth, etc. with the final compressor discharging toa vessel.

The heat of compression in this process must be liberated and this addsa further difiicult problem to be handled as lowering the temperature ofthe compressed gas also lowers the pressure. Testing of any onecompressor is therefore diflicult and the multi-stage process isprohibitive costwise for test purposes.

Without test equipment, the building of new equipment and componentsassumes the aspect of a dangerous gamble and the present inventionsolves this problem by furnishing test equipment economically which canreach test pressures far higher than available commercially therebyenabling progress in equipment based on actual test at very highpressures under actual working conditions not possible heretofore.

The primary object of the present invention is to provide a method andapparatus for testing the performance and strength of components of highpressure gas compressors apart from a complete, multi-stage machine.

Another object of the invention is to substitute two or more vessels aspressure staging means effective to eliminate staging compressors togain the desired suction pressure.

3,091,116 Patented May 28, 1963 "ire Another object of the invention isto provide pressure vessels which can be easily cooled and inexpensivelyconstructed to contain the very high pressures under test with maximumsafety.

Another object of the invention is to provide vessels having a lowvolume so that only minimal supply of test gas is consumed, making thetest very economical.

Another object of the invention is to provide such a method andapparatus which is inexpensive to operate and construct and which willgive definite results in a minimum of test time.

Briefly, the present invention, in its method aspects includes charginga compressor cylinder under test with a quantity of inert gas, such asfrom a previously pressurized bottle source, compressing the gas anddischarging it into at least two independent, closahle vessels,successively isolating one of the said vessels from the other, using theisolated vessel as an intermediate pressure supply in the suctioncircuit for the compressor while discharging into the other remainingload vessel, recharging the isolated vessel, and repeating the stepsuntil the pressure in the remaining load vessel equals or exceeds therated Working pressure of the compressor. Thereafter, the remaining loadvessel which contains gas at working pressure is connected as a closedcircuit to the compressor, a manually or automatically controlled valvebeing utilized to permit expansion of the trapped gas down to apredetermined suction pressure, while the compressor continues todischarge at high pressure into the same circuit.

In the accompanying drawings forming a part of the application:

FIG. 1 is a diagrammatic view of an apparatus, with parts in section,embodying the present invention, and capable of carrying out my newmethod.

Referring to the drawing, the present invention is shown in conjunctionwith the performance and strength testing of a compressor cylinder 10and its associated valves, the compressor having a conventionalclose-fitting high pressure plunger or piston. The valves are not shownin detail. A line leading to the suction valve is indicated generally at11 and a line leading from the discharge valve generally by thereference numeral 12. A purge connection 13 having a shutoff valve 14interconnects the lines v11 and 12 during the start of a test ashereinafter described.

Provision is made for charging the compressor cylinder as well as theremainder of the system with an inert gas such as nitrogen. The chargingline is indicated at 15 and is connected to the suction line 11 or cutoff therefrom by a valve 16. The charging gas may be stored in aconventional bottle 17 under pressure of, for example, 1000 p.s.i.g.

A plurality of isolated vessels, two in the form shown, are provided,and at first both may be connected to the compressor to act as receiversfor the compressor dis charge; then one vessel acts as a source ofsupply for the compressor suction while the compressor continues todischarge into the other vessel as a receiver.

One of the vessels, designated 20, may conveniently comprise a coil ofheavy wall tubing capable of withstanding an internal pressure equal toor greater than the highest pressure to which the compressor will betested. For example, if the test pressure is to be 100,000 p.s.i.g. thetubing may have an inside diameter of inch and an outside diameter of 1%inches. Such tubing will readily hold the desired pressure.

The vessel 20, referred to as a load vessel hereinafter is connected tothe compressor discharge line 12 by a line 21 having a shutoff valve 2'2therein, in series with a check valve 23 opening in the direction of thevessel 20. The load vessel 20 is also connected to the suction sideferred to hereinafter as a storage vessel, is connected to thecompressor discharge line 12 by line 31 having a shutoff valve 32therein, and to the suction line 11 of the compressor by a line 33having an adjustable orifice 34 and a shutoff valve 35 in series. Bymanipulation of the valves as hereinafter described, the presentinvention provides for the accumulation of gas under an intermediatepressure such as 16,000 to 20,000 p.s.i.g. in the storage vessel 30.Tubing having an inside diameter of /2 inch and an outside diameter of1% inches will Withstand these pressures.

' Because of the substantial energy imparted to the gases bycompression, provision is made for water cooling the vessels '20 and 30,for example by immersion ina suitable tank 37 through which water may becirculated.

From the foregoing it can be seen that the vessels 20 and 30 may beselectively connected to suction and discharge and selectively isolatedfrom suction and discharge, singly and in combination, as desired toaccomplish accumulating the very high test pressure in stages.

The operation of the parts so far described is as follows:

All of the valves are opened and the system purged in any suitablemanner so that all air therein is replaced with nitrogen (or otherprocess gas such as ethylene), either from the bottle 17 or some lowpressure source. After purging, the valve 14 in line 13 directly betweensuction ill and discharge 12 is closed and valve 16 remains openedfeeding gas from the bottle 17 via line 15 to the compressor 10. Valves25 and 35 in the lines 24 and 33, respectively, leading to compressorsuction 11 are closed and all other valves are open so that both vessels20 and 30 received compressed gas from the discharge line 12 via lines21 and 31 respectively. The compressor is now operating with a suctionpressure equal to the bottle pressure, for example 1000 p.s.i.g. If thecompression ratio of the compressor is to 1, the discharge pressure willbe 10,000 and pumping continues until bothvessels 20 and 30 contain gasat nearly this pressure. the drop in temperature.)

The next step is to disconnect the bottle 17 and use the storage vessel30 as a supply source for the compressor suction at increased suctionpressure while the compressor continues to discharge into the load.vessel 20.

Valve 16 in the line is now closed to cut off the bottle 17; valve 25 inline 24 remains closed to isolate the high pressure load vessel from thesuction line 11; valve 32 in line 31 is closed to isolate storage vessel30 from the compressor discharge 12. Valve 22 in line 21 remains openbetween the discharge line 12 and the load vessel 20.

Valve 3-5 is opened to connect the storage vessel 30 with the compressorsuction line 1 1.

The compressor is now operating with a suction pressure in theneighborhood of 10,000 p.s.i.g. supplied by storage vessel 30 via line33 and discharging into the load vessel 20 via line 21 at nearly tentimes this pressure. Due to the small volume capacity of the storagevessel 30, a large volume of gas at the high discharge pressure is notrequired; however, the discharged gas will expand down somewhat in thenow twice pressurized load vessel The next step in the process is toisolate the load vessel 7 (There will be some drop in pressure due tohigh intermediate pressure. Thus, when the pressure in the storagevessel 30 is down to some intermediate pressure, for example 5000p.s.i.g., valve 35 is closed to the suction side and valve 32 is openedto the discharge side and valve 16 in the bottle line 15 is reopened.Valve 25 remains closed in line 24 between suction line 11 and loadvessel 20. The compressor once again takes gas at the bottle pressurefrom line 15, compresses it into line 31 and recharges thestorage'vessel 30 to approximately 10,000 p.s.i.g. When this vessel isagain filled to the desired pressure, valve 16 from the bottle isclosed, valve 32 in line 31 from discharge line 12 is closed, valve 35in line 33 to suction 11 is reopened so that the recharged storagevessel 30 again becomes the supply for the suction side of thecompressor system.

The charging and partial exhaustion of the storage vessel 30' continuesuntil the high pressure vessel 20 contains gas at the desired testpressure, such as 100,000 p.s.i.g. Thereafter, the storage vessel 30inlet valve 32 and outlet valve 35 are closed, and the high pressureload vessel 20 adjustable orifice 26 and outlet valve 25 is manipulatedto give a suction pressure in lines 24 and 11 of about 10,000 p.s.i.ig.,the gas being taken from the high pressure load vessel 20. Thecompressor thereafter discharge 'gas back into the load vessel 20through line 21, check valve 23, and valve 22. It will be seen that thegas is now circulating from and to the load vessel 20 and that all ofthe compressor components are operating at the desired high pressurewhich may be equal to or greater than those encountered in service.

The present invention in its method aspects includes initially supplyinginert gas at the lowest supply pressure to the suction side of acompressor, compressing the gas in the compressor and discharging at ahigher intermediate pressure to at least two pressure accumulating ves-It includes disconnecting initial gas supply to the compressor,isolating said vessels from one another, consels.

transfer means to the compressor discharge, again furnishing initial gassupply to the compressor suction, again compressing the gas into thetransfer means, again disconnecting initial gas supply to thecompressor, again connecting the transfer means to the compressorsuction as supply, again connecting compressor discharge to the finalmeans, and again compressing the gas from the transfer means to thefinal means.

It includes then repeating the steps as stated until the final pressureaccumulation load means is at the desired very high pressure therebyproducing a very high pressure load under which the compressor randother equipment receives actual test.

The invention contemplates having as many interme diate pressuretransfer means or vessels as desired such as six or more wherein thefirst compression from the initial gas source raises all the vesselssuch as six to an intermediate pressure. supply for the next fivewherein the working pressure rises; the second is then used as supplyfor the next four wherein the pressure rises again; and the vessels areout off sequentially until the fifth is used as supply for the lastvessel wherein the pressure rises to the final very high load pressure.

It will thus be seen that the vessels represent steps in pressure andupon recharging the first vessel from the original supply, gas in thefirst can be compressed to the second, from the second to the third, andso on to obtain the final very high load pressure.

The invention includes means whereby the testing of high pressurecylinders is economical and it is to be particularly noted that only asmall volume of gas is re- The first vessel is then used as quired tooperate the cylinder 10 under actual load con ditions as the coils ofthe storage vessels 20 and 30 may be as short and their inside diameteras small as desired commensurate with the volume needed for testing thecylinder or other equipment under test.

Up to the present time testing has not been possible economically aspressurizing the gas circuit up to suction pressure has required manystaged compressors with as many as six stages being required to supply8000 p.s.i.g. suction pressure for cylinders having only 35,000 p.s.i.g.discharge pressure.

While only one embodiment of the invention has been disclosed anddescribed in detail, it is obvious that many changes may be made in thesize, shape, detail, and arrangement of the various parts and steps ofthe invent-ion Within the scope of the appended claims.

I claim:

1. Apparatus for testing high pressure fluid compressors and likeequipment under conditions and pressures at least equal to normalworking conditions and pressures comprising,

(a) a suction line leading to the equipment under test,

(b) a discharge line leading from said equipment,

() an ultimate pressure load vessel,

(d) at least one intermediate pressure accumulator storage vessel,

(e) -a source of gas under relatively low initial pressure,

(7) lines leading from said discharge line to all of said vessels,

(g) lines leading from all of said vessels to said suction line,

(h) a charging line leading from said source to said suction line,

(i) separately operable and closable valves in all said lines forselectively connecting and isolating said source of gas relative to saidsuction line and for selectively connecting and isolating said vesselsrelative to each other and fluid compressors and like equipment, and

(j) a pressure reducing valve interposed in the line between saidultimate pressure load vessel and said suction line,

(1) disposed to reduce the high pressure of gas in said load vessel to apredetermined suction pressure for said equipment when said load vesselis connected to both said suction line and said discharge line in a highpresusre circuit.

2. A method of testing a high pressure compressor and like equipment atpressures at least equal to normal Working pressures comprising,

(a) compressing gas from a source into a system including at least twovessels to establish in said vessels an intermediate pressure,

(12) isolating one of said vessels from the remaining vessels,

(0) compressing gas from said isolated vessel into said remainingvessels,

(d) recharging said isolated vessel to said intermediate pressure,

(e) repeating steps (c) and (d) until the pressure in said remainingvessels equals or exceeds the normal working pressure,

(1) connecting said remaining vessels with said compressor in a closedcircuit to act as a source for said compressor and to receive gasdischarged therefrom, and

(g) reducing the presusre of gas flowing from said load vessel tosubstantially the normal suction pressure of said compressor.

3. A method of testing a high pressure compressor in accordance withclaim 2 and the additional step of removing heat from said vesselsduring operation.

References Cited in the file of this patent UNITED STATES PATENTS

1. APPARATUS FOR TESTING HIGH PRESSURE FLUID COMPRESSORS AND LIKEEQUIPMENT UNDER CONDITIONS AND PRESSURES AT LEAST EQUAL TO NORMALWORKING CONDITIONS AND PRESSURES COMPRISING, (A) A SUCTION LINE LEADINGTO THE EQUIPMENT UNDER TEST, (B) A DISCHARGE LINE LEADING FROM SAIDEQUIPMENT, (C) AN ULTIMATE PRESSURE LOAD VESSEL, (D) AT LEAST ONEINTERMEDIATE PRESSURE ACCUMULATOR STORAGE VESSEL, (E) A SOURCE OF GASUNDER RELATIVELY LOW INITIAL PRESSURE, (F) LINES LEADING FROM SAIDDISCHARGE LINE TO ALL OF SAID VESSELS, (G) LINES LEADING FROM ALL OFSAID VESSELS TO SAID SUCTION LINE, (H) A CHARGING LINE LEADING FROM SAIDSOURCE TO SAID SUCTION LINE, (I) SEPARATELY OPERABLE AND CLOSABLE VALVESIN ALL SAID LINES FOR SELECTIVELY CONNECTING AND ISOLATING SAID SOURCEOF GAS RELATIVE TO SAID SUCTION LINE AND FOR SELECTIVELY CONNECTING ANDISOLATING SAID VESSELS RELATIVE TO EACH OTHER AND FLUID COMPRESSORS ANDLIKE EQUIPMENT, AND (J) A PRESSURE REDUCING VALVE INTERPOSED IN THE LINEBETWEEN SAID ULTIMATE PRESSURE LOAD VESSEL AND SAID SUCTION LINE, (1)DISPOSED TO REDUCE THE HIGH PRESSURE OF GAS IN SAID LOAD VESSEL TO APREDETERMINED SUCTION PRESSURE FOR SAID EQUIPMENT WHEN SAID LOAD VESSELIS CONNECTED TO BOTH SAID SUCTION LINE AND SAID DISCHARGE LINE IN A HIGHPRESSURE CIRCUIT.